The .NET Framework is Microsoft's comprehensive and consistent programming model for building applications that have visually stunning user experiences, seamless and secure communication, and the ability to model a range of business processes. The Microsoft .NET Framework 4 redistributable package installs the .NET Framework runtime and associated files that are required to run and develop applications to target the .NET Framework 4.

The .NET Framework 4 works side by side with older Framework versions. Applications that are based on earlier versions of the Framework will continue to run on the version targeted by default. Version 4.5.1 built upon successes of the previous milestone releases v4 (which among other things enabled developers to optimize their apps for parallel computing or distributed systems) and v4.5 (which for the first time enabled developers to start developing Metro-style apps for Windows 8, Windows RT and Windows Phone software environments).

The .NET Framework for PC is a development platform for building apps for web, Windows, Windows Phone, Windows Server, and Microsoft Azure. It consists of the common language runtime (CLR) and the .NET Framework class library, which includes a broad range of functionality and support for many industry standards.

Microsoft .NET Framework provides many services, including memory management, type and memory safety, security, networking, and application deployment. It provides easy-to-use data structures and APIs that abstract the lower-level Windows operating system. You can use a variety of programming languages with the .NET Framework, including C#, F#, and Visual Basic.

The .NET Framework comes with Windows PC, enabling you to run .NET Framework applications. You may need a later version of the .NET Framework than comes with your Windows version.